European buckthorn – an alien invader

Hey there, time traveller!
This article was published 06/08/2019 (2323 days ago), so information in it may no longer be current.

This story begins with a robin, waxwing, or house sparrow visiting a mountain ash tree in my yard a few years ago.

At least one bird had eaten the fruit from another species before its arrival. That fruit contained a laxative. Nature took its course and my feathered friend “planted” the seeds from European buckthorn (Rhamnus cathartica) under my mountain ash. The same story is unfolding along the Seine River.  

By the time I noticed, one seed had become a small tree. European buckthorn is not welcome in my yard. It is an invasive, non-native species. It grows very fast, produces lots of fruit, and has no natural control mechanisms (insects or disease). It was introduced in Wisconsin in the mid-1800s. Since then, it has invaded natural habitats in southern Canada — including Winnipeg’s urban forests, parks, prairies, and riverbanks.

Buckthorn is difficult to remove once it gains a foothold. I have cut my alien invader for several years now but the stump still sprouts new stems every spring.

Buckthorn produces dense shade. It alters the soil by adding high-nitrogen litter or chemicals that interfere with the germination and growth of native plants. Left unchecked, buckthorn displaces native species including chokecherry, pincherry, and wildflowers. A thicket of buckthorn can reduce native plant establishment by 90 per cent.

Winnipeg has been removing this species from the city’s riverbanks since 1998. Nature Manitoba, Save Our Seine, and other stewardship groups, play an important role in the control of this alien invader. Here’s how you can help.

Step 1: Learn to distinguish European buckthorn from native species (chokecherry, red osier dogwood) and non-invasive ornamentals (cotoneaster). It has distinctive leaf veins and bark.

Step 2: Remove buckthorn from your property. Report buckthorn you find on City property — especially on riverbanks. Volunteer to remove buckthorn on city land.

• Remove fruit-bearing plants first. Like willows, each buckthorn plant is either male or female. Remove female trees before the fruit ripens. This reduces on-site replacement and seed dispersal. Seeds are viable for about five years. Double-bag fruit for disposal.

• Remove buckthorn seedlings from the understory when they are small. Approximately 90 per cent of fruit falls below the parent trees, creating a thick stand of buckthorn with no biodiversity.

• Harvest wood from remaining buckthorn shrubs and trees for carvers.

Step 3: Replace buckthorn with native species. Studies have shown that planting Manitoba maple reduces the recurrence of this persistent alien invader.

Michele Kading is a community correspondent for St. Vital and the executive director of Save Our Seine.